What your missing is the freeze plug adapter that turns the freeze plug hole into a 3/4 threaded port.
And I have not found anyone that sells the adapter separately.
I had the same problem 28 or so years ago with my L2250, went to an automotive store and bought a in line heater that I installed in the bottom radiator hose. I turn it on about 30 min. before starting, and it never let me down yet.